Thursday, Aug. 11 update: the U.S. Drought
Monitor again this week lists 10% of the state in "Severe Drought," only 1%
"Abnormally Dry," and the rest of the state "Moderate Drought" in spite of more
frequent rain. 58% of CT rivers and streams have seriously low flows,
a small improvement from last week. Record low flows are still being
reported from 11 out of 83 stream gages (list is below).
Groundwater levels showed almost no improvement. A return to
more normal Summer rain may have started (see below).

News media is reporting our 30-day rain deficit has been
erased for much of the state, but many areas still have 30-day rain deficits of 1 to 2
inches with small areas up to 3 inches. Even where the the heaviest rain occurred, groundwater remains low
because not all heavy rain can soak into the ground. The 60-day rain deficit still
ranges from 1 to 5 inches across the state.

Streamflow continues to fall to seriously low levels between rain storms
because long-term rainfall has been a lot less than what we normally get, which causes groundwater levels
to drop. These topics are discussed
in more detail below. As described in previous
Know Your Flow! updates, the CT DPH issued the first Drought Advisory since 2010.
They cite the low rainfall but emphasize that public water supplies are doing
fine for now. Some public water supply companies are voluntarily asking for
water conservation due to lack of rain. The June 2016 monthly report from the
CT Department of Public Health, however, reported no restrictions, with state reservoirs at an average 91% of their capacity,
ranging from 73% to 100%. The advisory, however, does not mention that between-storm streamflow continues to drop.

Stream gages normally show pulses of above-average flow when it rains, then below average between storms.
Only a few of the records show Connecticut's streams rising above average at all during storms; most are barely reaching average, and a few have not even
come close to average. Dry conditions that cause flow to be below average more than it is above will affect stream life if these conditions continue for too long.
For a review of the localized relationship between streamflow and precipitation, see below.

Groundwater: The water level in streams and rivers between storms
depends on the flow of water out of the ground into the stream channel. The higher the water table, the more water is available to keep streams flowing. During a drought, smaller upland streams dry up faster than the larger rivers (see the graph below). Groundwater levels recovered during
the first three months of the year but have been dropping ever since.
An occasional brief, powerful rainstorm does not do much to help groundwater
levels rise. The rain falls faster than the ground can absorb, and thus much of
it becomes stormwater runoff. In that situation, public water supply systems
that depend on reservoirs are affected less than those with wells because the
runoff is collected by the reservoir.

Recent rains produced little or no improvement at the seven real-time monitoring wells run by the US Geological Survey (USGS).
Six of them report levels lower than 75% of their records for the date,
including five that are lower than ANY or that station's records. This continues a possible pattern of the last four years in which normal water levels in winter and spring have alternated with below-average in summer and fall. What is worrisome, however, is that the below-normal levels got worse each of those four years. Four years is not long enough to make any statistically valid conclusions about climate, however, and those station records only go back seven to 14 years. It was hoped that
the El Nino might have broken the
pattern (if there is a pattern), but the El Nino ended in May. USGS manually measures other wells once a month or so, and a quick look at those records verified the possibility that the abnormally low yearly pattern seen in the real-time data may be getting worse.

Precipitation.
In the areas where their 30-day deficit has been erased by recent heavy
rain, streamflow is expected to drop quickly because not all the rain soaked
into the ground to supply the rivers between storms. The National Weather Service Advanced Hydrologic Prediction Service
at this link (choose CT from the state drop-down list to see current data) shows
that over the last 60 days most of CT has received 50% to 75% of what we
normally get. Though some areas did get more than 75% of their normal
rainfall, no areas got more more than 90%. Some areas of the state only got 25%
to 50% of normal.

The dire situation last year (see below)
was caused not only by less total rainfall than normal over a long period of
time but also by the intensity of the rain we did get.

Rain? For most of the last six months,
storm tracks have brought most precipitation out to sea. Recently though, the
short-term and 16-day forecasts show a possible return to more normal Summertime
precipitation as thunderstorms and storms systems track over Connecticut. Normal
precipitation will not end the drought due to the serious long-term rain
deficit, but it could keep it from getting worse.

The NWS Climate Prediction Center's
1- and 3-month prognostications give equal chances for normal or above average or below average precipitation. These forecasts said nearly the same thing for most of the dry period last year, yet we consistently got less than normal precipitation.

Driest Streams and Rivers in CT(with USGS gaging stations)

On Aug 11, 48 out of 83 stream gages on the
USGS map of the
Connecticut area had less water flowing in them than 75% of their records
for the date.
To see their current
status, click on the stream name. Those in bold red were below the lowest daily
average recorded for that station for the date (11 of 83).

Meanwhile, parts of Coppermine Brook in Bristol were drawn down to rocks and dirt, as shown in the photo below taken Dec. 11 in Bristol. The sandy ditch in the foreground is the stream channel. Bristol Water Company and New Britain Water Company have eight registered diversions near Coppermine or its tributaries with a combined registered water withdrawal of 36.6 million gallons per day (source: CT DEEP). Company representatives report they do not withraw anywhere near that much water. Bristol Water says they stopped pumping from their well near this photo for a day but with no apparent effect on the stream. This is a perennial stream with a state Trout Management Area below where this picture was taken. Click on the photo for a full-screen version in a new tab.

This graph plots the rate of flow on Sept. 4 as a percentage of the median for each stream gage. For example, a dot at the 40% line means that stream that day was flowing at 40% of what could be considered normal for that date. The few rivers and streams flowing at or above 100% of their median rate are mostly those with flows managed by dam releases.&

Some General Flood Information:

When floodwaters fill the part of the stream channel that is called a floodplain, the water may find that someone has built a building or two in the channel. The water then saturates and fills any leach fields, often flushing untreated sewage out into the flow.

The floodwaters also find these really nice holes in the ground called wells to flow down into. All kinds of interesting things can be delivered to the bottom of the well, such as the aforementioned sewage, and soil, bugs, leaves, pesticides such as weed killer and insect poison, even the dog droppings from the backyard.

Very important: Any well that was flooded should be pumped and flushed out thoroughly and the system sanitized or "shocked."

There are places in Connecticut where the storm drains and the sewage pipes are combined into one system. With high rainfall, many of these combined pipes are designed to overflow into rivers and streams so the wastewater treatment plants are not overwhelmed. You really do not want to be downstream when raw untreated human sewage is entering the water. The DEEP has a map of Combined Sewer Overflows that shows the six urban areas where these can occur. Zoom in to any of them to see exactly where the combined flow may enter streams and rivers. Not every rain event is enough to cause these overflows, but it's a good idea to avoid contact with the water downstream from them after significant rain.

Unless you are an expert paddler, do not attempt to canoe or kayak on floodwaters; there are usually one or two fatalities per year. Our Connecticut Water Trails website and the webpages of the many paddler groups in the state all have good safety procedures. Here is a good article.

Streamflow Graphs and Storms

As the graphic to the right illustrates, where a storm moves across the state, the streams show flows that peak above their averages for this time of year but then quickly drop. The streams that maintain healthy flows between storms are those draining the parts of the state where there has been decent rainfall or those controlled by managed dams.

How quickly the flow drops after each rainstorm is unique for each stream, because it depends on how much water soaked in to increase the groundwater baseflow. In watersheds with lots of impervious roads, roofs, parking lots, patios, and compacted soil in lawns, a lot of the rain typically flows over the surface or through storm drains directly into the streams, leading to flooding problems far more often than in watersheds with mostly natural surfaces. Their streamflow then drops quickly after the storm ends, and the flow levels off far lower than in streams whose watersheds have more natural surfaces.

Recently there has been much discussion of what constitutes a "100-year-storm" or a "50-year storm." These traditional terms can be misleading unless you keep in mind they are an old-fashioned way of describing probablities. A "100-year" rainfall event means that in any year there is a 1% chance of that rate of rainfall.

Here is a map showing that in Connecticut we have a 1% chance of getting 7 to a little over 8 inches of rain in a 24-hour period, depending on where you are in the state. (Image source: http://precip.eas.cornell.edu/)

Comparing this to Table 7.2 (copy below) of the CT Stormwater Manual, we note that the design criteria for managing runoff possibly should be updated if we are building our landscape to control the flow from a 100-year-storm.

Drought pics

Photos by Joan Smith GOSA taken 9/20/2015 at The Merritt Family Forest in Groton. The stone slab bridge lies over Eccleston Brook, which had only a few puddles despite last week's downpour. The muddy bottom is also part of EB, further downstream. The photo with the two upright stone slabs is Cowslip Brook, a tributary to EB, and the wooden bridge traverses another small tributary to EB, flowing from a vernal pool. Used with permission.

News article: Researchers reveal cost-effective path to drought resiliency (July 21, 2016) "Published in San Francisco Estuary & Watershed, the study reveals the costs and benefits of using groundwater recharge and storage across the state. This process, known as "managed aquifer recharge," or MAR, can incorporate co-benefits such as flood control, improved water quality and wetland habitat protection. The study found the median cost of MAR projects is $410 per acre-foot (the amount of water required to cover an acre of level land at a depth of 1 foot) per year. By comparison, the median cost of surface water projects is five times more expensive -- $2,100 per acre-foot."